As a steam power cycle system that cycles a working fluid, while heating and cooling it, and causes the working fluid repeating a phase change to work, thus obtaining a power, there is known a basic type of Rankine cycle that is provided with an evaporator, an expander (turbine), a condenser and a pump, and utilizes as the working fluid a pure substance such as water.
However, in using the steam power cycle as a power generating equipment, etc., a temperature of both a high-temperature heat source and a low-temperature heat source in the steam power cycle is lower than a boiling point of water, in particular, in the application to a power generation apparatus by an ocean thermal energy conversion, a waste heat recovery power plant, or a power generating apparatus using a hot spring water. In case where a difference in temperature between the heat sources becomes smaller, there has conventionally been proposed, as an alternative to Rankine cycle that used water as the working fluid, a steam power cycle such as the so-called Kalina cycle that uses, as the working fluid, a mixture of water and a substance such as ammonia having a lower boiling point than water, or a mixture of a plurality of kinds of substances having a lower boiling point than water, i.e., a non-azeotropic mixture, which may make a phase-change at a temperature zone lower than the boiling point of water, so as to permit an appropriate phase change of the working fluid to convert effectively a heat into a power. An example of such a conventional steam power cycle is described in JP 57-200607 A and JP 7-91361 A.